Electro-acoustic delay-line



Nov. 28, 1961 G. G. scARRoTT ELECTRO-ACOUSTIC DELAY-LINE:

3 Sheets-Shes?l 1 Filed Aug. 17, 1959 FIG.

FIG.3.

FIG.

la/V" FIG.

IN VENTOR GORDON GEORGE SCARROTT Yea/Immma/m 'am ATTORNEKS Nov. 28, 1961 G. cs. scARRo'r-r ELEcTRo-Acousnc DELAY-LINE 3 Sheets-Sheet 2 Filed Aug. 17, 1959 OUTPUT FIG.

IN VENTOR GORDON GEORGE: 5c ARROTT ATTORNEYS Nov. 28, 1961 G. G. scARROT'r ELECTRO-ACOUSTIC DELAY-LINE 5 Sheets-Shea?l 3 Filed Aug. 17, 1959 FIG-9.

FIC-1.10.

INVENTOR GORDON GEORGE SCARROTT ATTORNEYS United States Patent() 3,011,136 ELECTROACUSTIC DELAY-LINE Gordon George Scarrott, Manchester, England, assignor to Ferranti Limited, Lancashire, England, a company 'of Great Britain Filed Aug. i7, 1959, Ser. No. 836,844 Claims priority, application Great Britain June 6, 1955 9 Claims. (Cl. S33- 30) This invention relates to electro-acoustic delay-line of the kind used to provide a predetermined time delay between input and output pulses of electric energy. The term pulse as used throughout this specification is intended to include any' waveform having a leading or trailing edge abrupt enough to mark an instant of time.

Such a delay-line usually consists of an elongated conductor of longitudinal stress-waves in the form of a wire at each end of which is an electro-acoustic stress-wave transducer for thek inputv and output pulses respectively. The term wire should be understood to include a rod or the like and the term delay-line to include the combination of the wire and the input and output transducers.

The input transducer is usually designed toset up a longitudinal stress-wave in the Wire in response to energisation by an electric input pulse. The output transducer is designed to supply the electric output pulse in response to energisation by the stress-wave set up by the input transducer after the interval occupied by the wave in travelling from one transducer to the other.

A well-known type of input transducer for this purpose consists of the combination of a coil surrounding a short length of wire of magnetostrictive material, such as nickel, which also serves as part of the stress-Wave conductor. Energisation of this coil effects a local distortion of that part of the wire in the field of the coil in the usual magnetostrictive manner and this in turn sets up a longitudinal lstress-wave in the wire.

'I'he corresponding output transducer may be a similar combination of coil -and magnetostrictive wire, with the addition of a permanent magnet or other means for setting up a field through the coil. The presence of the received stress-wave in that part of the wire in the lield causes a change of the flux linking the coil and so induces an output pulse.

It is also known to provide the input transducer with a magnet or the like to polarise it by setting up a constant afield through the coil; the steepest part ofthe magnetic characteristic of the wire may thus be brought into use.

A disadvantage of the above arrangements is that unless the wire is straight the longitudinal stress-waves are subjected to appreciable dispersion, which at any point on the wire is inversely proportional to the square of the radius to which the wire is bent -at that point.

An object of the present invention is to provide an acoustic delay-line which is cheap and simple to manufacture, robust in construction, reliable in operation and substantially insensitive to temperature changes.

Another object is to provide a delay-line which is capable of undistorted transmission of pulse signals with a predetermined delay which is constant for allfrequencies within a relatively wide band. f

A further object is to provide an acousticgdelay-line particularly suitable for digital storage purposes which is of curved form rather than straight but in which the Stress-waves are not subjected to appreciable dispersion, thereby affording the maximum storage capacity in a lgiven space. i

Still another object is the provision of an electroacoustic delay-line wherein the electric input pulses are converted into torsional stress-waves inthe wire of the line and said stress-waves are in turn converted at the out- .-7

In accordance with the present invention an electrov acoustic delay-line comprises a wire for propagating torsional stress-waves, an input torsional stress-wave transducer s and an output torsional stress-wave transducer located at diiferent axial positions' on the wire, each of which transducers includes a plurality of elongated mem- .bers of magnetostrictive material secured to the wire to extend tangentially from areas of contact which in that converter are located at vthe same axial position on the wire and are spaced around it at equal angular distances, the inputs transducer .including also electromagnetic means for setting up longitudinal stress-waves in the said members thereof, means for electrically pulse-energising said electromagnetic means to cause longitudinal stresswavesto reach the wire simultaneously in the same peripheral direction from each said member of the input transducer, .thereby setting up in the wire a torsional stress-wave travelling to the output transducer, the output transducer including also electromagnetic means for responding electrically to longitudinally stress-waves in the said members of the output transducer, and connections for deriving the electrical output of said last-mentioned electromagnetic `means to provide a response to a torsional stress-wave set up as aforesaid. Y

Where the wire is naturally straight, it may be disposed in a curved configuration within the elastic limit of the wire without subjecting the torsional Waves to any apprea ciable dispersion. The term naturallystraight wire as used herein means a wire which when unconstrainedtakes Aup a ,configuration which is either absolutely straight, or so` nearly so thatthe resulting small dispersion of torsional waves. is negligible from the standpoint of pulse distortion, and which must be continuously restrained when disposed in a curved contiguration. Although an appreciable amount of dispersion may be tolerable in some delay-line installations, it is generally undesirable because dispersion broadens the pulses put into the line and may cause overlapping of the output pulses to such an extent that they lose their identities and cannot be distinguished from one another. The low dispersion characteristic of delaylines embodying the present invention is therefore advantageous in increasing the storage capacity of the line.

There should be an acoustic match betweeneaeh of the elongated magnetostrictive members and the wire,

g firstly to ensure a substantially loss-free transfer of energy produce spurious pulses at the output of the delay-line.

' Where the input transducer includes two elongated n' magnetostrietive members extending in the same direction from the wire from diametrically opposite areas of contact with the wire, the electromagnetic means of this transducer may include means `for polarising at least one of the members so that the longitudinal stress-waves which travel to the Wire from these members are in opposite sense'sand so reach the wire in the same peripheral direction.

In the accompanying drawings:

lFIGURE. 1 is a schematic diagram of a delay-line in accordance with the invention;

FIGURESZ yand 3 are simplified diagrams of input and output torsional stress-wave transducers suitable for the delay-line of FIGURE l; v

FIGURE 4 shows a modied form of the delay-line of FIGURE l;

FIGURES 5 and 6 show alternative forms of torsional stress-wave transducers;

`FIGURE 7 is a plan view of one structural form of delay-line embodying Vthe invention with the case cover removed;

FlGURE 8 is an end elevation of the delay-line of FIGURE 7 looking from the right in the latter ligure with the end wall of the case broken away;

FIGURE 9 is an enlarged cross-sectional View of the input transducer taken substantially on the line 9 9 in .FlGURE 7;

FIGURES 10 and l1 are an enlarged plan view and side elevation, respectively, of the input transducer subassembly of the delay-line of FIGURE 7, FIGURE ll being partially in section along the line 11-11 in FIG- URE l0; and

FIGURE l2 is an enlarged cross-sectional view taken substantially on the line 12--12 in FIGURE 7 showing one of the supporting brackets by which the delay-line wire is maintained in the desired curved configuration.

In carrying out the invention according to one form by way of example, an electro-acoustic delay-line consists of a length of a naturally straight wire 11 of uniform diameter (see FIG. l) made of an alloy capable of low loss propagation of torsional stress-waves and having a low temperature coeiiicient of time delay, i.e., not more than about iSXlO-G per degree centigrade, at the ends of which wire are located the input and output torsional stress-wave transducers A and B respectively. Nickel-iron-titanium alloy and Ni-Span C are examples of alloys that may be used for the wire 11.

The input transducer is shown in detail in FIG. 2, the wire 11 being depicted end-on with a diameter much exaggerated for clarity. The transducer includes two elongated members of magnetostrictive material in the form of two like nickle strips 12 of rectangular cross section welded to extend tangentially from areas of cOntact at the surface of the wire which are spaced around the wire at equal angular distances; that is to say, the areas of contact are diametrically opposite one another. These areas are located at the sameaxial position on the wire; that is to say, the centres of the two areas lie in the same radial plane. The area of contact of each fstrip is located near one end of the strip on the broader surface thereof, this surface being parallel to the axis `of the wire, and the two strips extend from the wire in l'opposite directions.

The input transducer also includes electromagnetic means for setting up longitudinal stress-waves in the 'strips 12, in the form of a coil 13 carried by each strip` The two coils 13 are alike and are located at equal distances from the wire; they are connected in series or parallel t0 an apparatus 14- for simultaneous pulseienergization.

The output transducer is shown in FIG. 3, the wire 11 being again depicted end-on. This transducer is similar to -the input transducer, having nickel strips 15 extending 'tangentially from the wire and carrying coils 16, with Vthe addition for each coil of a permanent magnet 17 arranged to set up a field passing axially through the coil. The coils are electrically connected, in series or -parallel with one another, to the apparatus 18 to which Vthe output pulse is to be delivered. The combination 4of coils 16 and magnets 17 constitute electromagnetic means for responding electrically to longitudinal stresswaves in the strips 15.

In operation, each input pulse delivered by apparatus 14 to coils 13 causes the metal of each strip 12 to contract in known magnetostrictive mannerk and so sets up in the strip a longitudinal stress-wave travelling towards the wire. Owing to the like nature of the strips and the coils, longitudinal stress-waves of equal intensity reach the wire synchronously at diametrically opposite points but in the same peripheral direction. The effect is to produce in the wire a torsional stress-wave travelling towards the output transducer.

At the output transducer the arriving torsional wav sets up equal longitudinal stress-waves travelling out- Wardly along the two strips 15. Each coil 16 is thereby energised in the manner, described above, appropriate to known delay-lines using longitudinal waves, the energisation being synchronous because of the equal distances of the coils from the wire. An output pulse is thus developed.

Since the maintenance of pulse shape is of the first order of importance in delay-line operation, it is essential that the longitudinal stress-waves set up in the strips 12 of the input transducer arrive at the junction between said strips and the wire 11 substantially simultaneously so that these waves, which are separately identical, may add arithmetically and stimulate a torsional stress-wave of exactly the same shape and width as the individual longitudinal waves. To illustrate the importance of this feature, it is desirable that a delay-line embodying the present invention adapted to transmit pulses 1 microsecond long be limited to a maximum permissible variation in pulse width of 1/10 microsecond. If the times of arrival at the wire 11 of the longitudinal stress-waves from the strips 12 are not substantially simultaneous but should differ by more than 3A0 microsecond, the resulting torsional stress-wave in the wire and the electric output pulse delivered to apparatus 18 would be proportionately inaccurate. For example, if the two longitudinal stress-waves set up in the input transducer were displaced in time by an amount equal to the width of the input pulse, the resulting torsional stress-wave and output pulse would be twice the original width, an obviously intolerable condition for ldelaydine operation. Furthermore, should the longitudinal stress-waves arrive at the wire `at diierent times, the resulting action on the wire would not be a purely torsional couple, but would contain a transverse wave component which would be propagated along the wire at a dilferent speed from the torsional component and would result in a spurious pulse arriving at the output transducer at a different time from the main torsional pulse.

It will be evident that inaccuracies in the output pulses will also result if the coils 16 of the output transducer are not energised substantially simultaneously by the longitudinal stress-waves set up in strips 1S.

it can be demonstrated mathematically that where, in accordance with the present invention, the wire is naturally straight it lmay be disposed in a curved configuration without subjecting the torsional waves to any appreciable dispersion so long as the extent of curvature is within the elastic limit of the wire. A dat spiral, as shown in FIG. 4 (where A and B are again the transducers and 11 the wire), is a convenient coniiguration. The space-saving and other advantages of being able to use the wire thus curved are obviously considerable. The minimization of dispersion is also advantageous in that it increases the storage capacity of the delay-line. The result is that a curved delay-line embodying the invention provides the maximum amount of storage in any given amount of space.

For the reasons mentioned above, it is necessary that at each transducer there should be an acoustic match between the strips and the wire. A match is attained where the dimensions and characteristics of these components are such as to satisfy the expression where A and r are the sectional area of each strip and the radius of the wire, respectively, to the same dimensions, G1 is the shear modulus and W1 the density of the wire, E2 is the Youngs modulus and W2 the density 0f the strips, and n is the number of strips.

Each strip -12 of the input transducer may also be polarised, either by a permanent magnet 19 as indicated in FIG. 2, or by a direct current through the coil, to bring the steepest part of the magnet characteristic of the strip into use. In such an arrangement it is necessary to connect the coils 13 so that as the result of their pulse energisation the magnetostrictive contraction due to the magnets is either increased in both ot strips 12,

or decreased in both. l'[his ensures that the longitudinal stress-waves reach the wire in the same peripheral direction.

The strips 12 of the input transducer need not extend in opposite directions from the wire but may extend in the same direction. Such an arrangement is shown in FIG. 5, Where 11 is the wire, Zland 21 are the strips, and 22 and 23 are the coils. ln thiscase one of the coils, say coil 22, must be given a polarising field, as by a permanent magnet 24, of opposite sense to the field set up by the pulse applied to coil 22 so that the magnetostrictive contraction in strip 20 due to magnet 24 is reduced by that pulseinstead of increased. As the pulse in the other coil 23 causes a contraction in the other strip 21, longitudinal stress-waves of opposite sense in the two strips travel to the wire in a push-pull manner, as indicated by the arrows, and so cause yparticle motion in the same peripheral direction at the wire, thereby setting up a torsional stress-wave as before.

F[he other strip 21 may also be polarised, as indicated in FIG. at 25, to bring the steepest part of the magnetic characteristic of the strip'into use. it is then necessary to apply the pulse to coil 23 so as to increase the magnetostrictive contraction due to magnet 25. Magnet 24 may in fact serve to polarise both strips, it the coils are connected so that the fields set up by them when pulse-energised respectively increase the `contraction in one strip and decrease it in the other strip.

The arrangement of FIG. 5, where both coils are polarised, may be used for an output transducer, provided that the coils are interconnected so thatthe induced voltages do not oppose one another.

instead of having two strips, a transducer may have three or more, provided the areas Vof contact are spaced at equal angular distances'round the wire. An arrangethe wire, 26 the strips, and 27 the coils. The equal anguwire forming the spiralis maintained sufliciently large to prevent yexceeding the elastic limit of the wire.` For example, to provide a delay of 1000 microseconds for all frequencies within a band-.of approximately i500 kilocycles per Second centered at 1000 kilocycles per secpulses at a repetition rate of l megacycle per second.

ment with three strips is shown in FlG. 6, where 1l is lar distances 2S are here 120 degrees, instead of 180 degrees as inl the embodiments previously described. There is no need for the output transducer to have the same number of strips as the input transducer.

It is not essential for the coils of the input transducer to be located at equal `distances from the wire. lr', however, they are not so located, it is necessary to pulseenergise the coils at `dilerent times, rather than simultaneously, to ensure that the respective longitudinal stresswaves reach the wire at the same time. To effect this, the coil or coils nearer the wire should of course be pulsed later than the other coil or coils.

Referring now to the structural embodiment of the invention Aillustrated in FIGS. 7-l2, the delay-line shown therein comprises as its principal elements a length of naturally straight'wire 31 coiled in theV form of a flat spiral, an input transducer assembly 32 connected to the end of Wire 31 at the inside of the spiral, and an output transducer assembly 33 connected to the other end of the wire, all of said elements being suitably mounted in a case 34 which is normally provided with a cover (not shown).

The Wire 31 is made of a material which is capable of propagating torsional stress-waves with a minimum transmission loss and ywhich has a lofw temperature coeflicient of time delay such that the delay and output waveshape will be substantially independent of temperature changes. In a delay-line of the structure illustrated, it has been found that the desired results can bey obtained by using a wire made of a constant modulusv wrought nickel alloy, such as Ni-Span C, having a uniform diameter of .030 inch, a Youngs modulus of 27x10(i and an elastic limit in bending of 210,000 pounds per square inch. With a Wireof these characteristics, a

temperature coe'lcient of time delay of ilXlO"6 per degree Centigrade can be attained.

In order to ensure that the torsional stress-waves set un in the wire 31 are transmitted without appreciable dispersion, the radius of curvature of that portion of the inasmuch as wire 31 is naturally straight, it is necessary to positively restrain thefwire in the spiral configuration shown in FlG. 7, as long as the curvature of the 4wire does not result in bending i-t beyond the-elastic limit. For this purpose, a plurality of supportbrackets 35 are provided in such numbers and positions as to receive and hold the vwire 31 in the desired configuration.

As shown best'in FlG. l2, each bracket 35 consists of a vhorizontal base 36 which is riveted or otherwise suitably secured to the bottom of case 34, and a vertical ilange 43*] having formed in its upper edge a plurality of laterally spaced slots 38 the bottoms of which are of circular cross section of substantially `the same size as the wire 31. `The brackets 35 are made of an insulating material which yis preferably flexible, such as molded nylon, so

thatV the Widthof the upper end of each slot 38 may beA made slightly vless than the diameter of wire 31, and yet, by deformation of the material of the llange, the wire may be forced downwardly into the circular bottom end of the slot andL there held against movement inv any direction transverse to the wire axis. v

f The input transducer-t assembly 32 which `is connected to the inner end of delay-line wire 31 includes two elongated members 39 of magnetostrictive material which are secured to and ext-end tangentially in the same direction from the end of wire 31, fa transducer sub-assembly 40 adapted to set up longitudinal stress-waves in members 39`which reach the wire simultaneously in the same pe- ,'ripheral direction and thereby ,set up correspond-ing `torsional stress-waves in said wire, a damping termination 41 for the ends of members 39 remote from the wire, and a transducer mounting plate 42 which is riveted or otherwise suitably secured to the bottom of case 34 inside the spirally coiled wire 31.

Although the elongated magnetostrictive members 39 may take various forms, it is preferable to form each such member of two or more tapes or wires bunched together so as to'improve the eiiiciency of the transducer by` reducing eddygcurrent losses under the transducer coil while still retaining the maximum cross-sectional area of magnetic material within the coil, and also attaining the desired acoustic match at the junction between Vthe -magnetostrictive members and the delay-line wire.

1n the embodiment'otEgFlGS. 7-12, each member 39 consists of two relatively thin, flat nickeltapes each having a width of .020 inch and a thickness of ,.002 inch, the ,tapes being superposed with their at sides in contact Vyface of one tape of each pair in contact with the wire,

and the tapes extend perpendicularly to the Iwire in the same direction, one above the other. In accordance with the preceding disclosure, the cross-sectional area, the Youngs modulus and the density of the tapes`39 are so related to the radius, shear modulus'and density of the wire 31 that there is acoustic match at the junction therebetween, thereby ensuring maximum eiciency of y energy transfer at the junction and also avoiding reflections at this point which would produce spurious pulses at the output of the delay-line.

In order to properly position the junction between wire 31 and magnetostrictive members 39 with respect to the transducer sub-assembly 40, mounting plate 42 includes a pair of upwardly projecting bifurcated guides 43 which receive and hold the portion of the wire immediately adjacent the inner end thereo-f, and a horizontally extending ciamping bracket 44 is provided which overlies the junction and cushions it against undesired mechanical vibration by means of a pair of foam rubber Ipads 45 interposed between the clamping bracket and the mounting plate. Bracket 44 may be supported in the desired position in any suitable manner, as by a screwed connection to the upper end of a vertical stand-off carried by mounting plate 42. The end portion o-f wire 3l which extends1 through guides 43 may be enclosed as shown in FIG. 7 in a sleeve of suitable insulating material, such as polythene plastic.

The transducer sub-assembly 4t2 comprises the electromagnetic means for setting up longitudinal stress-waves in the magnetostrictive members 39, and is also adjustable lengthwise of said members in order to effect slight variations in the delay period of the delay-line. As shown best in FIGS. 9-ll, the body of sub-assembly 40 consists of a coil cell 46 in the |form of a rectangular block of insulating material, such as polystyrene plastic, slidably supported on mounting plate 42 and having two vertically separated, horizontally extending bores 47 in which are housed energising coils 48 and 49, and another bore 56 parallel to and equidistantly spaced from bores 47 wherein a polarising permanent magnet 51 is housed. Each of coils 48 and 49 is wound on a hollow bobbin 52 of polystyrene plastic or other suitable insulating material, the enlarged heads of which have a forced rit in the bores 47 and are provided with V-shaped notches in their periphelies through which the ends of the coil winding extend. The members 39 pass freely through the yaxial holes in the bobbins and are thus surrounded by the coils.

Projecting laterally from one side of coil cell 46 is a shelf 53 carrying three electrical terminals 54, 55 and 56 to which the ends of the coil windings are connected. In the embodiment illustrated, coils 48 and 49 are similarly oriented in the bores 47, the starting ends of the coil windings are separately connected to terminals 54 and 55, respectively, and the finishing ends of both coils are connected together to terminal 56. Terminals 54 and 55 are also connected by a pair of lead wires 57 to the `input terminals 58 and 59, respectively, of the delay-line which are insulatedly mounted on the wall of case 34. VWith this arrangement, input pulses applied to terminals 58 and 59 will pass through coils 48 and 49 in opposite directions and thereby set up magnetizing fields of opposite sense which, imposed on the steady polarising lields set up by lmagnet 51, simultaneously producel magnetostrictive contraction of one o-f members 39 and'elongation of the other. The result is that longitudinal stress-waves of opposite sense are set up in members 39 at points which are equidistant from the wire 31. Consequently, the longitudinal stress-waves reach the wire 31 simultaneously and, -by their push-pull effect, produce torsional stress-waves in the wire which travel to the outer end thereof where the output transducer assembly 33 is connected.

In onder to enable micrometric adjustment of energising coils 48 and 49 lengthwise of magnetostrictive members 39 so as to vary the delay provided by the line, coil cell 46 is provided with a ange 60 which extends laterally from the side of the cell block opposite shelf 53 and is screwed or otherwise suitably connected to a mating flange 61 projecting laterally from the body of a drive nut .62; Like coil cell 46, drive nut 62 is slidably supported on mounting plate 42, and is provided with a threaded bore 63 having its axis parallel to those of coil bores 47 and magnet bore Sti of the coil cell. An elongated lead screw 64 passes through bore 63 and is rotatably supported at one end in a circular opening in a ange 65 extending upwardly from mounting plate 42 adjacent damping termination 4l, and at the other end in a slotted flange 66 which extends upwardly from mounting plate 42 adjacent clamping bracket 44. The portion of lead screw 64 which is supported in slotted ilange 66 is of reduced diameter so as to provide shoulders engaging the opposite sides of flange 66 which prevent axial movement of the lead screw when the latter is rotated to feed drive nut 62 and coil cell 46 toward or away from wire 3l. Clamping bracket 44 is provided with a horizontally extending portion 67 which is adapted to frictionally engage an Unthreaded portion of lead screw 64 immediately adjacent slotted ange 66 and thereby act as a brake to prevent accidental rotation of the lead screw. in the delay-line shown in FIGS. 7-12, lead screw 64 is of sufficient length to permit a variation of 6 microseconds in the delay provided by the device.

The outer ends of the tapes forming magnetostrictive members 39 are supported by the damping termination 4i in the manner indicated in FIGS. 7 and 9 so as to absorb the longitudinal stress-waves which travel away from wire 3l and thus prevent reflections that would produce spurious pulses at the output end of the line. As shown, termination 41 comprises three elongated damping pads 68, 69 and 7G piled one on top of the other with the bottom pad 68 resting on transducer mounting plate 42 and the top pad 79 surmounted -by a flanged cover plate 7i which is screwed or otherwise suitably connected to the upper ends of four supporting standoffs 72 iixed to and extending upwardly from mounting plate 42 through aligned openings in pads 63, 69 and 70.` 'Ihe damping pads are made of a resilient, compressible electrically insulating material, such as silicon rubber, and provide an acoustic wave absorbing support for the outer ends of ltapes 39 the lower pair of which is sandwiched between pads 68 and 69 while the upper pair is disposed between pads 69 and 70. The outer end portions of each pair of tapes are separated as indicated in FIG. 7 in order to improve the damping coupling between the tapes and the rubber pads, and may be additionally insulated Iby en- Vclosure within a very thin folded sheet 73 of insulating 39', 49', 41', etc., and therefore need not be described in detail. Suice it to say that the output transducer assembly differs from the input assembly only in that (a) lead screw 64 is slightly longer than lead screw 64 so as to provide for a variation in the delay of 8, instead of 6, microseconds; (b) mounting plate 42 and clamping bracket 44 4are of opposite hand to plate 42 and bracket 44; (c) the ends of all four magnetostrictive tapes 39' are grounded to the bottomI of case 34 by a conductor 74 and ground contact 75, the conductor 74 also being connected to a ground terminal 76 extending through the wall of case 34, and (d) the conductors 57 connect terminals 54 and 55' to the output terminals 77 and 78 of the delay-line which are insulatedly mounted on the wall of case 34 similarly to input terminals 58 and 59.

In operation, the torsional stress-waves travelling in wire 31, upon arrival at the output transducer 33, set

up equal longitudinal stress-waves of opposite sense inV f magnetostrictive members 39. The longitudinal stresswaves in turn simultaneously energise coils 48' and 49 and induce therein electrica-l output pulses identical in 'lil shape, width and repetition rateto the input pulses supplied to coils 48 and 49 of the input transducer.

Although each o f the delay-lines above described includes only one input transducer and one output transducer connected respectively to the opposite ends of the torsional stress-wave transmitting wi-re, the invention may also be embodied in a delay-line wherein additional transducers of the same construction :as those at the ends of the wire are Aconnected to the latter at intermediate points along the length thereof in order to provide different delay periods with the same line. In such a device, the delay-line wire may be tapped at any desired point alongits length bysmply spot welding thereto the magnetostrictive tapes of another transducer assembly.

It will be appreciated that a delay-line in accordance with the invention, in addition topossessing lthe important advantage of allowing the wire to be used in a curved configuration, has theadditional advantage that the torsional stress-wave transducers which form parts of it are simple and cheap to manufacture inY addition to being very efficient inioperation. v

This is a continuation-impart of application Serial No. 589,134, filed June 4, 1956, now abandoned.

What is claimed is:

l. An electro-acoustic delay-line comprising a naturally straight wire disposed in a curved coniguration within the elastic limit of the wire and capable of propagating torsional stress-waves without appreciable dispersion over a wide band of frequencies and having a low temperature coefficient of time delay, -a iirst magnetostrictive transducer for setting up vtorsional stress-waves in said wire at one position along the length thereof, and a second magnetostrictive transducer connected to said wire at a second position along the length thereof axially spaced from said first-named position `for converting the torsional stress-waves propagated in said Wire into electrical pulses, each of said transducers including a plurality of elongated members of magnetostrictive material. secured to and extending tangentially from said wire and said iirst transducer including means responsive to electrical pulse energy for setting up longitudinal stresswaves in said members which reach the wire substantially simultaneousi@ the dimensions and physical characteristics of said wire and of the magnetostrictive members'of said transducers being so related that there is a mechanical acoustic match between said members and said wire at the junctions thereof. 3. A delay-line as claimed in claim 2 wherein the crosssectional areas of said wire and said members, the shear modulus anddensity of said wire and the Youngs modulus and density of said members are so related as to satisfy the expression A nr G1 W1 I 271 E2 W2 wherein A and r `are the sectional area of each ymember and the radius of the wire, respectively, G1 is the shear modulus and W1 the density of the wire, E2 `is the Youngs modulus and W2 the densi-ty of said members, and n is the number of said members. Y

4. A delay-line as claimed in claim 2 wherein the input transducer includes two of said members extending in the same direction from the wire from diametrically opposite areas of contact with the wire, and wherein the v electromagnetic means of said input transducer includes ly in the same peripheral direction and thereby set up corresponding torsional stress-waves in said wire, the dimeans :for so polarising at least one of said two members that the longitudinal stress-waves setup in said members are of opposite sense.

5. A delay-line as claimed in claim 2 wherein each of said members of the input transducer is polarised.

6. An electro-acoustic delay-line comprising a naturallyy straight wire of uniform diameter disposed in a curved coniiguration within thev elastic limit of the wire and thereby capable of propagating torsional stress-Waves without yappreciable, dispersion over a wide band of frequencies, an input transducer and an output transducer located at different axial positions on the wire, each of said transducers including a plurality of elongated members of magnetostrictive material secured to the wire to extend tangentially from areas of contact located at the same axial position on the wire and spaced around it at equal angular distances, a coil surrounding each of said members of the input transducer for setting up longitudinal stress-waves therein, and a coil surrounding each yof said members of the output transducer for responding to longitudinal stress-Waves therein, the coils of said input transducer being located at-equal distances from the wire and being so connected for simultaneous pulse-energisatween each vof said transducers and said wire at the junction thereof.

2. An electro-acoustic delay-line comprising a natura 1y straight Wire of uniformdiameter disposed in a curved configuration within the elastic limit of the wire and capable of propagating torsional stress-waves without appreciable dispersion over a wide band of frequencies, an input transducer and an output transducer located at different axial positions on the wire, each of said transducers including a plurality of elongated mem-bers of magnetostrictive material secured to the wire to extend tangentially from areas of contact which in that transducer are located at the same axial position on the wire and are spaced around it at equal angular distances, electromagnetic means for setting up longitudinal stresswaves in the said members of said input transducer, means for electrically pulse-energising said electromagnetic means, said electromagnetic means being so positioned relative to said members and said wire and being pulse-energised in such a manner that the longitudinal stress-waves reach the wire substantially simultaneously in the same peripheral direction from each member of said input transducer and thereby set up in the wire torsional stress-waves which travel to the output transducer, and electromagnetic means responsive electrically to longitudinal stress-waves in the said members of the output transducer for producing electrical output pulses corresponding tot the torsional stress-waves set up in said wire,

7. An electro-acoustic delay-line comprising a natural- Y ly straight wire disposed in acurved configuration within the elastic limit of the wire and capable of propagating` torsional stress-waves without appreciable dispersion over a wide band of frequencies, an input transducer and an output transducer located at different axial positions on said wire, each of said transducers including a plurality of elongated members of magnetostrictive material secured to said wire to extend tangentially from areas of contact located at the same axial position on the wire and spaced around it at equal angular distances, means responsive to electrical pulse energy for setting up longitudinal stress-waves in the magnetostrictive members of said input transducer which reach the wire in the same peripheral direction and set up corresponding torsional stress-waves in said wire, and means responsive to longitudinal stress-waves in the magnetostrictive-members of said output transducer for producing electrical output 1 l pulses corresponding to the torsional stress-Waves set up in said Wire, the dimensions and physical characteristics of said Wire and of the magnetostrictive members of said transducers being so related that there is a mechanical acoustic match between said members and said wire at the junctions thereof.

8. An electro-acoustic delay-line comprising a naturally straight Wire disposed in a curved configuration Within the elastic limit o-f the wire and capable of propagating torsional stress-Waves Without appreciable dispersion over a Wide band of frequencies, an input transducer operably connected to said wire at one point along the length thereof and responsive to electrical pulse energy for setting up torsional stress-Waves in said Wire, and an output transducer operably connected to said wire at a second point along the length thereof and responsive to the torsional stress-wavcs in said Wire for producing electrical output pulses corresponding to said torsional Stress-Waves.

9. A delay-line as claimed in claim 8 wherein lat least one of said transducers includes a plurality of elongated members of magnetostrictive material secured to the wire to extend tangentially from areas of contact which in that transducer are located at the same axial position on the wire and are spaced around it at equal angular distances, the dimensions and physical characteristics of said wire and of the magnetostric-tive members of said transducer being so related that there is a mechanical acoustic match between said members and said wire at the junetions thereof.

' References Cited in the tile of this patent v UNITED STATES PATENTS 2,430,013 Hansell Nov. 4, 1947 2,495,740 Labin et al. Jan. 31, 1950 2,799,832 Niederman et al July 16, 1957 2,800,633 Roberts et al. July 23, 1957 2,810,888 George et al. Oct. 29, 1957 2,828,470 Mason Mar. 25, 1958 2,906,971 Mason et al Sept. 29, 1959 FOREIGN PATENTS 714,627 Great Britain Sept. 1, 1954 

